FUNDAMENTALS IN TOOTH PREPARATION

By- Priyesh Kharat

DEFINITION OF TOOTH PREPARATION

Tooth preparation is the mechanical alteration of a defective, injured, or diseased tooth to receive a restorative material that re-establishes a healthy state for the tooth, including esthetic corrections where indicated and normal form and function.

OBJECTIVES OF TOOTH PREPARATION

Remove all defects and provide necessary protection to the pulp

(2) extend the restoration as conservatively as possible,

(3) form the tooth preparation so that under the force of mastication the tooth or the restoration or both will not fracture and the restoration will not fracture & the restoration will not displaced, and

(4) allow for the esthetic and functional placement of a restorative material.

TOOTH PREPARATION TERMINOLOGY

Tooth preparation walls Internal wall –An internal wall is prepared

surface that does not extend to external tooth surface.

Axial Wall - An axial wall is an internal wall parallel with the long axis of the tooth

Pulpal Wall- A pulpal wall is an internal wall that is perpendicular to the long axis of the tooth and occlusal of the pulp.

External Wall- An external wall is a prepared (cut) surface that extends to the external tooth surface. Such a wall takes the name of the tooth surface (or aspect) that the wall is toward

. Floor (or Seat)- A floor (or seat) is a prepared wall

that is reasonably flat and perpendicular to the occlusal forces that are directed occlusogingivally (generally parallel to the long axis of the tooth Examples are the pulpal and gingival walls.

Enamel Wall- The enamel wall is that portion of a prepared external wall consisting of enamel

Dentinal Wall- The dentinal wall is that portion of a prepared external wall consisting of dentin, in which mechanical retention features may be located.

TOOTH PREPARATION ANGLES

Line angle. A line angle is the junction of two planal surfaces of different orientation along a line

An internal line angle is a line angle whose apex points into the tooth

An external line angle is a line angle whose apex points away from the tooth

Point angle – a point angle is the junction of three planal surface of different orietation

CLASSIFICATION OF TOOTH PREPARATION Class I Restoration All pit rand-fissure restoration are class I and

they are assigned to three groups. Restoration on Occlusal Surface of Premolars &

Molars. Restorations on Occlusal Two Thirds of the

Facial and lingual surfaces of Molars. Restoration on lingual Surface of Maxillary

Incisor

class II Restorations.

Restorations on Proximal surface of posterior teeth are Class II

Class III Restorations Restorations on the proximal surface of anterior teeth

that do not involve the incisal angle are Class III.

Class IV Restoration- Restorations on the proximal surfaces of anterior

teeth that do involve the incisal edge are class IV

Class V Restorations Restoration on the gingival third of the Facial or

lingual surface of all teeth( except pit-and-fissure lesions) are Class V

Class VI Restorations- Restorations on the incisal edge of anterior teeth or

the occlusal cusp height of posterior teeth are class VI

INITIAL AND FINAL STAGES OF TOOTH PREPARATION

Initial tooth preparation stage Step 1: Outline form and initial depth Step2 Primary resistance form Step3 Primary retention form Step4 Convenience form

Final tooth preparation stage Step 5 Removal of any remaining infected dentin or

old restorative material (or both), if indicated Step 6: Pulp protection, if indicated Step 7: Secondary resistance and retention forms Step 8: Procedures for finishing external walls Step 9: Final procedure--cleaning, inspecting sealing

INITIAL TOOTH PREPARATION STAGE

Initial tooth preparation is the extension and initial design of external walls of preparation at a specified limited depth so as to provide access to the caries or defect, reach sound tooth Structure, resist fracture of the tooth restorative material from masticatory forces principally directed with the long axis of the tooth,and retain the restorativc material in the tooth .

STEP 1: OUTLINE FORM AND INITIAL DEPTH

Def- Establishing the outline form means(1)

placing the preparation margins in the positions they will occupy in the final preparation except for Finishing enamel walls and margins and (2) preparing an initial depth of 0.2 to 0.8 mm pulpally of the DEJ Postion or root-surface position

PRINCIPLES:-

(1) all friable or weakened enamel should be

removed

(2) all faults should be included and

(3) all margins should be in a position to afford good finishing of the margin of the restoration.

FEATURES…

1) Preserving cuspal strength 2) preserving marginal ridge strength 3) Minimizing faciolingual extension 4) using enamelopasty 5) Connecting two close faults or tooth

preparation 6) Restricting the depth of the preparation

into dentin to a maximum of 0.2mm for pit & fissure caries and 0.2 to 0.8 mm for axial wall of smooth surface caries.

STEP 2. PRIMARY RESISTANCE FORM

Def:- Primary Resistance form may be defined as

the shape and placement of preparation walls that best enable the restoration and the tooth to withstand, without Fracture, masticatory forces delivered principally in the long axis of the tooth.

PRINCIPLE__

1) to use the box shape with a relativity flat floor which helps the tooth resist occlusal loading by virtue of being at right angles to the forces of mastication that are directed in the long axis of the tooth

2) to restrict the extension of the external walls to allow strong cusp and ridge areas to remain with sufficient dentin support

3) to have a slight rounding of internal line angles to reduces stress concentration in tooth structure

4) to cap weak cusps and envelope

5) to provide enough thickness of restorative material to prevent its Fracture under load and

6) to bond the material to tooth structure when appropriate.

FEATURES:- 1) Relatively flat floors

2) Box shape

3) Inclusion of weakened tooth structure

4) Preservation of cusps & marginal ridges

5) Rounded internal line angles

6) Adequate thickness of restorative material

7) Reduction of cusps for capping when indicated

STEP3: PRIMARY RETENTION FORM

Def:-

Primary Retention form is the shape or form of the conventional preparation that resists displacement or removal of restoration by tipping or lifting forces.

STEP4: CONVENIENCE FORM.

Convenience form is the shape or form of preparation that provide for adequate observation, accessibility and ease of operation in preparing & restorating the tooth.

STEP 5: REMOVAL OF ANY REMAINING ENAMEL PIT OR FISSURE, INFECTED DENTIN, OR OLD RESTORATIVE, IF INDICATED.

Removal of any remaining enamel pit or fissure infected dentin, or old Restorative material is the elimination of any infected carious tooth Structure or faulty restorative material left in the tooth after initial tooth preparation .

ANY REMAINING OLD RESTORATIVE MATERIAL SHOULD BE REMOVED IF ANY OF THE FOLLOWING CONDITIONS ARE PRESENT_- _

1) The old material may affect negatively the esthetic result of the new restoration.

2) the old material may compromise the amount of anticipated needed retention.

3) Radiographic evidence indicates caries is Under the old material.

4) The tooth pulp was symptomatic preoperatively or

5) The periphery of the remaining old restorative material is not intact.

STEP 6: PULP PROTECTION, IF INDICATED

The reason for using traditional liner or bases is to protect the pulp or to aid pulpal recovery or both.

Other pulpal irritants that affect operative procedure are:-

1) Some ingredients of various materials 2) thermal changes conducted through restorative

materials, 3) force transmitted through materiel to the

dentin a) Galvanic shock and most importantly 5) The ingress of noxious products & bacteria

through microleakage.

Liners also may provide 1) A barrier that protects the dentin from

noxious agents from restorative material oral fluids

2) Initial electrical insulation 3) Some thermal protection

Ex- of bases include zinc phosphate, zinc oxide eugenol calcium hydroxide, polycarboxylate & glass ionomer

STEP 7… SECONDARY RESISTANCE & RETENTION FORMS

The secondary retention and resistance form are of two types…

1) Mechanical preparation feature Retention locks, Grooves & Coves. Groove Extensions, Skirts Beveled Enamel Margins. Pins, Slots, Steps, Amalgampins.. 2) treatments of preparation walls with

etching, priming &adhesive materials. Enamel Wall Etching Dentin Treatment .

STEP 8: PROCEDURE FOR FINISHING THE EXTERNAL WALLS

Finishing the preparation wall is the further development, when indicated, of a specific Cavo surface design & degree of smoothness or roughness that produces the maximum effectiveness of he restorative material being used.

Objectives: - 1) create the best marginal seal possible

between the restorative material and the tooth strcture.

2)afford a smooth marginal junction and 3) provide maximal strength of the tooth &

the restorative material at & near the margin

FEATURES-

1) the design of the cavosurface angle & 2) The degree of smoothness or roughness of

wall.

. Cavosurface angle of 90° produces maximal. Strength for the amalgam & the tooth. No bevels an placed at the cavosurface margin.

Beveling can serve useful purpose in tooth preparation

1) It produces a strong enamel margin 2) If permits a marginal seal in slightly

undersized. Casings.

STEP. 9: FINAL PROCEDURE: CLEANING, INSPECTING. & SEALING

The usual procedure in cleaning is to free the. Preparation of visible debris with warm water from the syringe & then to remove the visible moisture with a few light surges of air from the air syringe .

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